I recently purchased a Nivada Antarctic GMT for my significant other (as well as myself). The *original* Nivada Antarctic chronometers were worn in Operation Deep Freeze I, but the GMT version is a super weird watch made made about a decade later with no concrete relation to Deep Freeze. Based on my extensive research (read: cruising Google and hoping something of value was listed as a hit), it uses the same base movement, module, and case as the Enicar Sherpa-Jet. Additionally, it isn't a "true GMT" in the sense that a Rolex GMT-Master is; to my knowledge (I didn't want to try and break my new watch) the 24-hour GMT hand cannot be set independently of the 12-hour hand as the stem only has one setting position. Due to this, GMT is set by moving a rotating 24 hour bezel so the current time zone (UTC +/- X) is in the 12 o'clock position.
I'm clueless as to the production numbers of this watch. It appears to be rather uncommon- there are very few Google Image results of the watch, and they appear to be of the same 2 watches, one of the two being the watch I purchased. As is usually the case, it's been all but impossible to find any actual numeric values. Any information regarding production or anything else about this watch would be greatly appreciated!